Episodic dyspnea, lung inflammation, and in some patients, progressive irreversible airway dysfunction are characteristic of asthma. Experimental models that share many features in common with human asthma have shed much light on the mechanisms of these pathologic processes. Matrix metalloproteinases (MMPs) and serine proteases are up-regulated in asthma, thus understanding their roles as disease modifiers can potentially offer new opportunities for therapeutic intervention. This proposal will define the role of proteases in an acute asthma model and extend these observations to understand the cross-talk between immune and nonimmune cells in orchestrating inflammatory cell clearance from lung. We will address the functional significance of proteases by combined in rive and in vitro approaches. Specifically, the first aim will determine spatio-temporal regulation of proteases synthesized in the lung of mice exhibiting the asthma phenotype. We hypothesize a reciprocal relationship in which endogenous protease expression is essential for efficient Th2 cell development and recruitment and Th2 cells in turn determine airway protease expression. The second aim wilt determine the role of endogenous proteases in the progression of reactive stroma. Expression of proteases and airway inflammation, independent of the acute asthma phenotype, elicits reactive stroma formation, collagen deposition, and airway remodeling. We hypothesize that dysregulated airway protease activity modifies the asthma phenotype by accelerating, or preventing resolution of, airway matrix remodeling. Airway collagen synthesis, AHR, and goblet cell metaplasia in mice chronically challenged with antigen and protease inhibitors will be determined. Finally, in our expanded specific aim we propose to determine the role of MMPs in mediating inflammatory cell clearance in allergic lung disease. We have found that treatment of antigen challenged mice with a synthetic class-specific inhibitor of MMPs, result in massive accumulation of inflammatory cells concomitant with an increase in Th2 cytokines in the lung parenchyma. We hypothesize that MMPs modify the availability of chemoattractants and/or modify chemokine receptor expression, resulting in accumulation of inflammatory cells in the lung parenchyma. We will explore the novel concept that MMPs are required to establish such parenchyma-to-airway ("inside-out") chemotactic gradients and the functional consequences of the failure of these responses in allergic inflammatory lung diseases. Insight into this area of allergic inflammation will answer important questions on mechanisms of allergic airway disease. This work may serve as the foundation for future therapeutic studies that target a broad range of asthmatic patients.